Truf is a popular Indonesian trick-taking game with bidding. It has several characteristics that may seem unusual to Western card players - for example:
The name "truf" is probably derived from the Dutch troef, which means trump.
Truf is normally played by four people using a standard international 52-card pack (no jokers). It is possible for three to play, in which case one of the black suits is removed, leaving a pack of 39 cards.
In the play, the rank of the cards from high to low in each suit is A-K-Q-J-10-9-8-7-6-5-4-3-2.
After shuffling, all the cards are dealt to the players one at a time, so that each player has 13 cards. Any player may deal the first hand; subsequently the player with the lowest cumulative score should deal. If any player has a hand consisting entirely of numeral cards 2-10 or a hand consisting entirely of aces, kings, queens and jacks, the cards must be thrown in, shuffled again and redealt.
It is usual to play alternate deals counterclockwise and clockwise. The first deal is counterclockwise. Usually a complete game consists of 13 deals.
All players bid simultaneously by placing a card from their hand face down on the table. The rank of the card represents the number of tricks the player intends to take. Picture cards King, Queen and Jack represent no tricks, Ace represents one trick and numeral cards from 2 to 10 represent that number of tricks.
When everyone is ready all the bid cards are exposed. The suit of the bid card of the player who bid the most tricks is the trump suit for that hand. In case of a tie for most tricks bid, the suits rank from high to low: spades, hearts, diamonds, clubs and the highest suit in which most tricks are bid is trumps.
If the numbers of tricks bid by all the players adds up to more than 13, a "main atas" is played, in which the object is to take as many tricks as possible.
If the numbers of tricks bid by all the players adds up to less than 13, a "main bawah" is played, in which the object is to avoid taking tricks.
If the numbers of tricks bid by all the players adds up to 13 exactly, the highest bidder (the player whose bid determines trumps) must choose to increase or decrease all the bids by an equal amount. For example if the bids are 5,4,3,1 the player who bid 5 tricks might increase them to 6-5-4-2 and play a "main atas" or change them to 4,3,2,0 and play a main bawah. It is also possible to increase or decrease the bids by more than one trick - for example to 3,2,1,-1. It is possible for bids to become negative in this way.
Examples:
3, 
5, A, 
3. Diamonds are trumps and "main bawah" is played.
5, 5, 3, K. Hearts are trumps - the higher suit of the 5-trick bids. Since the total is exactly 13, the holder of the 5 must increase or decrease the bids. He decides to subtract one trick, so the bids become 4, 4, 2 and -1 and again a "main bawah" is played.After the bids, trump suit and mode of play are settled, the players take their bid cards back into their hands and the play begins.
The player who bid highest - the one whose bid card determined trumps - leads to the first trick. Each trick is won by the highest card of the suit led unless it contains a trump, in which case the highest trump wins. The winner of each trick leads to the next.
Players must follow suit (play a card of the same suit as the card led to the trick) if possible. A player who is unable to follow suit may play any card - a trump or a card of another non-trump suit.
If no trumps have yet been played, it is illegal to lead a trump to a trick, unless your hand contains nothing but trumps. Once a trump has been played (for example by a player who is unable to follow suit and chooses to trump), any card can be led.
Trumps led or played to a trick are always played face down. Cards of non-trump suits are always played face up. At the end of each trick, any trumps that are in it are turned face up, to find out who has won the trick.
At the end of the play, all players count their tricks and compare them to their bids. Different groups of players use different methods of scoring.
If a main bawah was played (total bids were less than 13):
A player whose bid is negative (because the winner of the bidding decreased the bids) will of course always lose points. For example if your bid is -1 and you take 1 trick, you lose 2 points; if you take no tricks you lose 1 points.
If a main atas was played (total bids were more than 13):
Example: North bids 4, East 5, South 0, West 3 so main bawah is played. North takes 4 tricks, East 3, South 0, West 6. Scores are North 0, East +2, South 0, West -3.
This is exactly the same as the first method, except that in a main bawah, a player whose bid is zero and who makes no tricks scores +5 rather than zero. This 5-point bonus applies even if the player originally made a positive bid, which was reduced to zero by the winner of the bidding when the bid total was 13. On the other hand if you originally bids zero but your bid was made negative by the winner of the bidding, you cannot score the 5-point bonus.
This is the same as the first method except that positive scores are increased by a multiplier. For example, if the multiplier is 2, a player who has bid 3 in a main atas would score -3 points for 0 tricks, -2 for 1 tricks, -1 for 2 tricks, 0 for 3 tricks, 2 for 4 tricks, 4 for 5 tricks, 6 for 6 tricks, 8 for 7 tricks, etc. A player who bid 4 in a main bawah would score 8 for 0 tricks, 6 for 3 tricks, ... , 0 for 4 tricks, -1 for 5 tricks, -2 for 6 tricks, etc.
It is possible to combine this method with the 5-point bonus for bidding and making no tricks as in method 2. This bonus remains 5 points - it is not affected by the multiplier.
Hamdanil Rasyid, who has played at university in Singapore and with fellow Indonesians in California, USA reports that many people use the following method of scoring, in which the aim is to win exactly the number of tricks you bid, and any other result gives a negative score:
If a main atas was played (total bids were more than 13):
Example: North bids 4, East 5, South 2, West 3 so main atas is played. North takes 4 tricks, East 3, South 0, West 6. Scores are North +4, East 2×(-2) = -4, South 2×(-2) = -4, West -3
If a main bawah was played (total bids were less than 13):
Some players allow more than one card to be used for a bid. The values of the cards are added to represent the number of tricks bid. If the cards of the winning bid are all in the same suit, this is the trump suit. If the winning bid contains cards of more than one suit there are no trumps. If there is a tie for highest bid a no-trump bid wins against a suit bid. In the unlikely event of a tie for highest bid between two bids of the same suit or two no trump bids, I suggest that whichever of those bids contains the highest single card should win.
Some play that a two-card bid must be for at least 5 tricks and a 3-card bid must be for at least 9 tricks.
Some players allow multiple card bids in which the values of bid cards can be added or subtracted at the bidder's choice to make up the total bid. Bid cards placed face down are added and bid cards placed face up are subtracted. Allowing subtraction makes the bidding easier, probably too easy: whatever your hand it will almost always be possible to find a combination of cards that can represent a feasible bid.
You can play a version of Truf online at JB Games. This version uses the fourth method of scoring described above, and also allows multiple card bids in which the card values can be added or subtracted.